
import json

def load_dataset(format, data_files):
    if format != 'json':
        raise ValueError(f"Unsupported format: {format}")
    
    if not isinstance(data_files, str):
        raise ValueError("data_files should be a string path to the JSON file")
    
    dataset = {'train': []}
    try:
        with open(data_files, 'r') as file:
            for line in file:
                data = json.loads(line.strip())
                dataset['train'].append(data)
    except FileNotFoundError:
        raise FileNotFoundError(f"File {data_files} not found.")
    
    return dataset
